1. Field of the Invention
The present invention relates to a plasma processing apparatus and a plasma processing method for processing an object to be processed such as a semiconductor substrate or the like with a plasma excited by radiating a microwave.
2. Description of Related Art
In a work for manufacturing a semiconductor device, a surface quality modifying process for modifying the surface material quality by nitriding or oxidizing the wafer surface, an ashing process for removing resist, a layer forming process for forming a thin layer by depositing materials such as an insulating material or the like on the wafer surface and an etching process for processing the thin layer formed on the wafer surface into minute patterns are carried out. Attention has been paid to an RLSA (Radial Line Slot Antenna) plasma processing apparatus as an apparatus for carrying out these processes.
An RLSA plasma processing apparatus comprises a processing chamber having an opened upper surface, and a dielectric plate disposed as closing the opened upper surface of the processing chamber. A cavity defined by the processing chamber and the dielectric plate serves as a processing cavity for plasma processing a semiconductor wafer as an object to be processed. Provided in the processing cavity is a wafer stage for mounting and holding a semiconductor wafer thereon. Further, disposed above the dielectric plate is a radial line slot antenna for radiating a microwave through the dielectric plate into the processing cavity.
For example, in the case of nitriding the surface of a semiconductor wafer using such an RLSA plasma processing apparatus, first, the semiconductor wafer is mounted on the wafer stage with the surface of the semiconductor wafer directed upwardly. Next, a process gas (for example, Ar/NH3) is supplied into the processing cavity, and thereafter a microwave is radiated from the radial line slot antenna toward the processing cavity. Thereby, a plasma of the process gas is generated in the processing cavity, and the surface of the semiconductor wafer mounted on the wafer stage is nitrided by the generated plasma.
The radial line slot antenna has a number of slots formed so as to be distributed in the whole region of the lower surface of the antenna, so that the microwave is radiated from the number of the slots. Consequently, in an RLSA plasma processing apparatus using such a radial line slot antenna, since a microwave can be radiated substantially uniformly in the processing cavity, a plasma of a process gas can be uniformly generated. Therefore, it is expected that the surface of a semiconductor wafer can be uniformly processed with the plasma.
However, in a conventional RLSA plasma processing apparatus, since the density of a plasma generated in the processing cavity is low, the processing rate is low. Consequently, such a conventional RLSA plasma processing apparatus cannot be used for manufacturing a semiconductor device in practice.